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<p class="purpose">An overview of the index module's role and abilities.</p>

<ul class="toc"><li><a href="P-wtmd.html#SP1">&#167;1. Prerequisites</a></li><li><a href="P-wtmd.html#SP2">&#167;2. The Index</a></li><li><a href="P-wtmd.html#SP4">&#167;4. Localisation</a></li></ul><hr class="tocbar">

<p class="commentary firstcommentary"><a id="SP1" class="paragraph-anchor"></a><b>&#167;1. Prerequisites.</b>The index module is a part of the Inform compiler toolset. It is
presented as a literate program or "web". Before diving in:
</p>

<ul class="items"><li>(a) It helps to have some experience of reading webs: see <a href="../inweb/index.html" class="internal">inweb</a> for more.
</li><li>(b) The module is written in C, in fact ANSI C99, but this is disguised by the
fact that it uses some extension syntaxes provided by the <a href="../inweb/index.html" class="internal">inweb</a> literate
programming tool, making it a dialect of C called InC. See <a href="../inweb/index.html" class="internal">inweb</a> for
full details, but essentially: it's C without predeclarations or header files,
and where functions have names like <span class="extract"><span class="extract-syntax">Tags::add_by_name</span></span> rather than just <span class="extract"><span class="extract-syntax">add_by_name</span></span>.
</li><li>(c) This module uses other modules drawn from the compiler (see <a href="../structure.html" class="internal">structure</a>), and also
uses a module of utility functions called <a href="../foundation/index.html" class="internal">foundation</a>.
For more, see <a href="../foundation/P-abgtf.html" class="internal">A Brief Guide to Foundation (in foundation)</a>.
</li></ul>
<p class="commentary firstcommentary"><a id="SP2" class="paragraph-anchor"></a><b>&#167;2. The Index.</b>All users of the Inform GUI app are familiar with the Index: it's a sort of
mini-website giving a detailed picture of the content of the story being
created. In the current design, there are seven colour-coded "pages", each
divided up into two or more parts called "elements".
</p>

<p class="commentary">In fact, this is only one of the possible "index products". It's also possible
to generate an EPS (encapsulated PostScript) file of a spatial map, for example.
</p>

<p class="commentary">Until 2021 the Index for a project was generated by the main <a href="../inform7/index.html" class="internal">inform7</a> compiler,
but a radical refactoring then moved the entire <a href="index.html" class="internal">index</a> module into <a href="../inter/index.html" class="internal">inter</a>
instead. Index products are now generated from trees of Inter code, not from
Inform projects as such:
</p>

<pre class="displayed-code all-displayed-code code-font">
<span class="plain-syntax">                      </span><span class="identifier-syntax">source</span><span class="plain-syntax"> </span><span class="identifier-syntax">text</span>
<span class="plain-syntax">                          |</span>
<span class="plain-syntax">                          | </span><span class="identifier-syntax">inform7</span>
<span class="plain-syntax">                         \|/</span>
<span class="plain-syntax">                      </span><span class="identifier-syntax">inter</span><span class="plain-syntax"> </span><span class="identifier-syntax">tree</span>
<span class="plain-syntax">                       /     \</span>
<span class="plain-syntax">               </span><span class="identifier-syntax">inter</span><span class="plain-syntax">  /       \  </span><span class="identifier-syntax">inter</span>
<span class="plain-syntax">    (</span><span class="identifier-syntax">final</span><span class="plain-syntax"> </span><span class="identifier-syntax">module</span><span class="plain-syntax">)   /         \   (</span><span class="identifier-syntax">index</span><span class="plain-syntax"> </span><span class="identifier-syntax">module</span><span class="plain-syntax">)</span>
<span class="plain-syntax">                    |           |</span>
<span class="plain-syntax">                   \|/         \|/</span>
<span class="plain-syntax">           </span><span class="identifier-syntax">generated</span><span class="plain-syntax"> </span><span class="identifier-syntax">code</span><span class="plain-syntax">     </span><span class="identifier-syntax">Index</span><span class="plain-syntax"> </span><span class="identifier-syntax">products</span>
<span class="plain-syntax">                    |</span>
<span class="plain-syntax">                    | </span><span class="identifier-syntax">inform6</span><span class="plain-syntax"> (</span><span class="identifier-syntax">or</span><span class="plain-syntax"> </span><span class="identifier-syntax">similar</span><span class="plain-syntax">)</span>
<span class="plain-syntax">                   \|/</span>
<span class="plain-syntax">       </span><span class="identifier-syntax">Executable</span><span class="plain-syntax"> </span><span class="identifier-syntax">products</span>
</pre>
<p class="commentary firstcommentary"><a id="SP3" class="paragraph-anchor"></a><b>&#167;3. </b>The <a href="index.html" class="internal">index</a> module has a very simple API: point it at a tree of Inter code,
say what sort of index you want, and go. See <a href="1-ia.html" class="internal">Indexing API</a> for the details,
though the details are not much more than that.
</p>

<p class="commentary firstcommentary"><a id="SP4" class="paragraph-anchor"></a><b>&#167;4. Localisation.</b>A new and somewhat experimental addition in 2021 is the ability to localise the
Index, that is, to produce an Index in a language other than English. This does
not of course aim to translate source text: simply to translate subheadings, notes,
and other fixed-wording text in the Index.
</p>

<p class="commentary">As a demonstration, try running a project with:
</p>

<pre class="displayed-code all-displayed-code code-font">
<span class="identifier-syntax">Use</span><span class="plain-syntax"> </span><span class="identifier-syntax">French</span><span class="plain-syntax"> </span><span class="identifier-syntax">language</span><span class="plain-syntax"> </span><span class="identifier-syntax">index</span><span class="plain-syntax">.</span>
</pre>
<p class="commentary">You should then find that the index has a French-titled Contents section &mdash; only
a couple of strings have been localised at present, and those not localised
revert to English, so the index still looks basically English. This is all really
just laying groundwork.
</p>

<p class="commentary">For how to write localisation files, see <a href="../html-module/2-lcl.html" class="internal">Localisation (in html)</a>, or follow
the example of <span class="extract"><span class="extract-syntax">inform/inform7/Internal/Languages/English/Index.txt</span></span>.
</p>

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